DOCS-3879: Document changes for 2.6 in date formatting

source/reference/glossary.txt

@@ -251,6 +251,10 @@ Glossary
       :term:`primary` on startup and in the event of a failure. See
       :ref:`replica-set-elections`.
 
+   unix epoch
+      January 1st, 1970 at 00:00:00 UTC. Commonly used in expressing time,
+      where the number of seconds or milliseconds since this point is counted.
+
    eventual consistency
       A property of a distributed system that allows changes to the
       system to propagate gradually. In a database system, this means
@@ -544,7 +548,7 @@ Glossary
       moving a document when it grows as the result of
       :method:`~db.collection.update()`
       operations. See :ref:`record-allocation-strategies`.
-      
+
    padding factor
       An automatically-calibrated constant used to determine how much
       extra space MongoDB should allocate per document container on disk.

source/reference/mongodb-extended-json.txt

@@ -118,16 +118,23 @@ Date
 
       * - .. code-block:: none
 
-             { "$date": <date> }
+             { "$date": "<date>" }
 
         -
 
         - .. code-block:: none
 
              new Date ( <date> )
 
-   ``<date>`` is the JSON representation of a 64-bit signed integer for
-   milliseconds since epoch UTC (unsigned before version 1.9.1).
+   In *Strict mode*, ``<date>`` is typically an ISO-8601 date format following
+   the template ``YYYY-MM-DDTHH:mm:ss.mmm<+/-Offset>``. When formatting
+   pre-:term:`unix epoch` dates, the format instead encodes as a string the
+   negative integer giving the number of milliseconds since epoch UTC:
+
+      ``{ "$date" : { "$numberLong" : "<date>" } }``
+
+   In *Shell mode*, ``<date>`` is the JSON representation of a 64-bit signed
+   integer giving the number of milliseconds since epoch UTC.
 
 Timestamp
 ~~~~~~~~~
@@ -368,5 +375,5 @@ NumberLong
         - .. code-block:: none
 
              NumberLong( <number> )
-   
+
    Number long is a 64 bit signed integer.

source/release-notes/2.6-compatibility.txt

@@ -394,10 +394,8 @@ Timestamp Format Change
 ~~~~~~~~~~~~~~~~~~~~~~~
 
 Description
-  Each message now starts with the timestamp formatted in
-  ``iso8601-local``, i.e. ``YYYY-MM-DDTHH:mm:ss.mmm<+/-Offset>``. For
-  example, ``2014-03-04T20:13:38.944-0500``. Previous versions used
-  ``ctime`` format.
+  Each message now starts with the timestamp format given in :ref:`2.6-time-format-changes`.
+  Previous versions used the ``ctime`` format.
 
 Solution
   MongoDB adds a new option :option:`--timeStampFormat` which supports
@@ -902,6 +900,20 @@ Solution
    Update :data:`local.system.replset.members[n].votes` with values
    other than 1 or 0 to 1 or 0 as appropriate.
 
+.. _2.6-time-format-changes:
+
+Time Format Changes
+-------------------
+
+MongoDB now uses ``iso8601-local`` when formatting time for many output purposes.
+This format follows the template ``YYYY-MM-DDTHH:mm:ss.mmm<+/-Offset>``. For
+example, ``2014-03-04T20:13:38.944-0500``.
+
+This change impacts anything using
+:doc:`Extended JSON </reference/mongodb-extended-json>` in *Strict mode*, such as
+:program:`mongoexport` and the :ecosystem:`REST and HTTP Interfaces
+</tools/http-interfaces>`.
+
 .. _2.6-compatibility-other-resources:
 
 Other Resources